Turmeric is a spice grown in India and other tropical regions of Asia. It has a long history of use in herbal remedies, particularly in China, India, and Indonesia. Turmeric or “yellow root” is a general term for plants and plant materials having a high content of curcuminoids, compounds that have a strong colouring effect and which are used extensively in the colouring of e.g. food products.
Curcumin, reddish orange and with two methoxy groups, is the principal curcuminoid of the popular Indian spice turmeric, which is a member of the ginger family (Zingiberaceae). Turmeric's other two curcuminoids are demethoxycurcumin, orange-yellow with one methoxy group, and bisdemethoxycurcumin, yellow and without a methoxy group. The curcuminoids are natural phenols that are responsible for the yellow color of turmeric.
Preparing solvent extracts of Curcuma plant materials, in particular rhizomes, provides an oleoresin comprising an essential oil of turmeric and curcuminoids. The oleoresin may subsequently be subjected to a crystallization step resulting in the obtainment of curcuminoid crystals of a relatively high purity and a liquid part. Liquid part included essential oil of turmeric, flavouring compounds, any impurities that remained in solution and, curcuminoids that did not crystallize. Essential oil of turmeric is isolated from the liquid part by steam distillation. The residual material that remains after the above separation of curcuminoid crystals and essential oil of turmeric consists mainly of uncrystallized curcuminoids. This residue is generally disposed of as a waste product of the industrial process.